Naphthenic base oil is base oil that has a viscosity index of 85 or less and in which at least 30% of the carbon bonds of the base oil are of a naphthenic type, according to ASTM D-2140.
Recently, naphthenic base oil is widely used in various industrial fields, including transformer oil, insulation oil, refrigerator oil, oil for processing rubber and plastic, fundamental material of print ink or grease, and base oil of metal processing oil.
Most conventional methods of manufacturing naphthenic base oil are conducted in such a manner that naphthenic crude oil having a high naphthene content (naphthene content: 30˜40%), serving as a feedstock, is passed through a vacuum distillation unit to thus separate a paraffinic component and then through extraction and/or hydrogenation units to thus separate an aromatic component and/or convert it into naphthene, after which impurities are removed.
However, these methods are problematic in that the essential use of the naphthenic crude oil, having a high naphthene content, as the feedstock encounters a limitation in the supply thereof, and furthermore, the extraction procedure for extracting the aromatic component must be conducted, undesirably decreasing the total product yield and deteriorating the quality of the product.
International Patent No. WO 2004/094565 discloses a method of manufacturing naphthenic base oil by subjecting mixed effluents of various processes, serving as a feedstock, to hydrofining to thus obtain an oil fraction, which is then stripped to separate only an oil fraction having a boiling point within a predetermined range, and then dewaxing the separated oil fraction. However, the above method is disadvantageous because, among the effluents of the hydrofining process, only a middle oil fraction, excluding a light oil fraction and a heavy bottom oil fraction, is used to produce the naphthenic base oil, undesirably decreasing the total product yield. Further, because the effect of the hydrofining process for removing impurities is not high, sulfur is contained in a large amount in the middle oil fraction, separated through stripping, undesirably remarkably reducing the activity and selectivity of a catalyst used for a subsequent dewaxing process.